1. Field of the Invention
This invention pertains generally to treatment of concrete washout waste, and more particularly to treatment of waste liquid associated with washout of concrete trucks and associated equipment on construction sites and at concrete batch plants.
2. Description of Related Art
Construction sites have long been identified as a large contributor to urban runoff pollution if the proper pollution prevention practices are not regularly performed. Construction materials washed into the storm drain have a direct impact on local waterways and habitat living in that environment.
The most common discharge into storm drains from concrete construction activity is the residue and contaminants from washing down equipment such as concrete trucks, pumps, mixers, chutes, hand tools and wheelbarrows. Other cementitious contaminants include washout from grout, mortar and stucco. Once released into a storm drain, the solids and sediments are not easily removed and the high pH and suspended solids of the waste are extremely toxic to aquatic wildlife.
Temporary washout areas with berms, haybales, linings and catchment systems are typically used on construction sites, but with poor results. These temporary sites are prone to leaking or flooding during rains. Evaporation or leaching as a method to remove the liquid waste is not environmentally safe or practical. Dumpsters and sludge boxes are also used to contain washout waste but are prone to leaking during use or during transport.
Some concrete trucks are equipped with a reclaimer system, a temporary storage for washout waste that is returned to the batch plant for recycling. These systems require valuable time for the operator to use and need ongoing maintenance to stay operational.
On some construction sites, individual plastic bags are used to contain washout waste. These small bags, typically about 5 gallons, are time consuming to use and usually require two persons to handle during washout activities. They may be left on the jobsite for several weeks exposed to the elements, rough ground, and puncture hazards.
Some existing systems transport the concrete waste to evaporation ponds or lagoons to evaporate the liquid and then bury, dispose or recycle the remaining solids. Evaporation ponds are subject to leaking high pH liquid with suspended solids and heavy metals into the environment. In some cases, pH treatment is performed in place to reduce the environmental risk of leaking evaporation ponds.